This invention relates to a liquid-liquid centrifugal extractor, and more particularly to the structure of means for distributing a liquid of smaller specific gravity and a liquid of larger specific gravity uniformly within the extractor and method of using the same.
The "liquid-liquid extractor" is an equipment wherein the two liquids of an original solution in which an extract being a noticed component is dissolved and an extractant which cannot be dissolved in the original solution and which dissolves only the extract are brought into direct contact and wherein the extract is caused to migrate into the extractant and is separated. Specifically, the centrifugal extractor brings the two liquids into contact by exploiting the difference of centrifugal forces based on the difference of the specific gravities of the two liquids.
The liquid-liquid centrifugal extractor is equipped with a rotor which is fixed to a shaft in a manner to be concentric therewith. The liquid of greater specific gravity (hereinafter, called the "heavy liquid") is introduced into the inner peripheral portion of the rotor, while the liquid of smaller specific gravity (hereinbelow, called the "light liquid") is introduced into the outer peripheral portion of the rotor. As the shaft and the rotor rotate, the centrifugal forces are generated in the two liquids. Owing to the difference of the specific gravities of the two liquids, the centrifugal forces developing in the respective liquids have different magnitudes. The heavy liquid moves from the inner peripheral side onto the outer peripheral side within the rotor and forms a heavy liquid continuous layer, while the light liquid moves from the outer peripheral side onto the inner peripheral side and forms a light liquid continuous layer. Meanwhile, the extract contained in one liquid dissolves into the other liquid and migrates with the latter liquid. In this way, the extraction of the extract is carried out.
In order to raise the extraction efficiency in such a centrifugal extractor, both the liquids need to be distributed so that the heavy liquid and the light liquid within the rotor may have uniform flows in the circumferential direction and the axial direction of the rotor without any maldistribution and that the contact area between both the liquids may be large. To this end, in a prior art, a plurality of perforated cylinders are arranged within the rotor concentrically with the shaft and at fixed intervals in the radial direction as means for distributing the liquids. An example of the means is illustrated in a drawing on page 119 of "CHEMICAL ENGINEERING, June 11, 1962". The perforated cylinder is provided with small holes at fixed intervals in the circumferential direction and the axial direction. The light liquid and the heavy liquid supplied into the rotor are respectively intercepted by the perforated cylinders to become uniform flows in the circumferential and axial directions, and pass through the small holes in the perforated cylinders to uniformly migrate within the rotor. In passing through the small holes, the liquids become droplets to increase the surface area and to enhance the extraction efficiency.
Depending on the capacity of the extractor, however, such a perforated cylinder becomes 1,000 mm or more in the diameter, 1,000 mm or more in the axial length and 1 to several mm in the thickness, and it is subjected by the rotation to a centrifugal force which is 1,500 times or more greater than the gravity. Due to this centrifugal force, the axial central part of the perforated cylinder expands. For this reason, a stream of the heavy liquid arises chiefly in the central part in the axial direction and a stream of the light liquid arises chiefly in both the end parts in the axial direction, so that the two liquids cannot contact sufficiently and that the extraction efficiency lowers. The cylinder is feared to damage due to the deformation, and the damage is dangerous.
Moreover, in case of the construction as stated above, one liquid is distributed by the perforated cylinder after having flowed into the continuous layer of the other liquid, which gives rise to the inconvenience that both the liquids pass through the same small holes in the opposite directions. In consequence, the flow resistances of the liquids become high, and the flow velocities become low. This is one of causes for a low extraction efficiency as will be described later.